The present invention generally relates to the field of radio frequency antennas, and more particularly to an antenna system that incorporates a stack of overlying dual element antennas in a single structure so that the bandwidth of the antenna system is the sum of the bandwidths of all the individual antennas.
A dipole antenna generally has about 20% bandwidth, depending on its actual configuration. Multiple bandwidth performance is conventionally achieved by employing separate dipole antennas that each cover a specific portion of the radio frequency spectrum. However, separate dipole antennas collectively tend to be bulky. Shipboard communications systems generally require multiple bandwidth performance. However, multiple antenna systems on board ships must compete for a very limited amount of space. Therefore, there is a strong need for an antenna system that provides multiple bandwidth performance in a compact package.
The present invention provides a wideband antenna system incorporates a stack of m antennas, Ai, where i is an index from 1 to m, m and i are positive integers, and mxe2x89xa72. Each antenna Ai includes: an electrically insulating substrate; opposed radio frequency elements mounted to the electrically insulating substrate such that the radio frequency elements of the antennas A2 through Am provide ground planes for antennas A1 through Amxe2x88x921; and a ground plane mounted to the substrate for antenna Am. In other words, each underlying antenna Ai provides a ground plane for the immediately overlying antennas. The bandwidth of the antenna system is generally the sum of the bandwidths of the individual antennas, thereby providing the antenna system with wideband performance characteristics in a compact package. However, it is to be understood that some of the bandwidths of the individual antennas may be continuous, overlapping, spaced apart, or some combination of the foregoing. The antenna system may also incorporate a frequency selective surface so that the antenna system is limited to detecting RF signals having particular bandwidth characteristics.
The invention may also be characterized as a wideband antenna system that comprises a stack of m antennas, where m is a positive integer, and mxe2x89xa72. Each antenna includes: a) an electrically insulating substrate: b) opposed first and second radio frequency elements mounted to the substrate: c) a ground feed electrically connected to the first radio frequency element: d) an excitation feed electrically connected to the second radio frequency element: and e) a ground plane mounted to the substrate of the mth antenna. The radio frequency elements of each antenna collectively have a unique total area and are mounted to the electrically insulating substrate. The radio frequency elements of the ith antenna provide a ground plane for the kth antenna, where i and k are positive integers 1xe2x89xa6kxe2x89xa6(ixe2x88x921) and 2xe2x89xa6ixe2x89xa6m. The total area of the first and second radio frequency elements of the ith antenna is greater than the total area of the first and second radio frequency elements of the kth antenna.
In another embodiment of the invention, antenna stacks may be radially distributed about an arcuate shaped structure such as a tube so that each stack has a unique field of view. This configuration allows the antenna system to detect or transmit RF signals to some or all of a broad region without having to rotate the antenna.
These and other advantages of the invention will become more apparent upon review of the accompanying drawings and specification, including the claims.